Control device for hydrostatic steering means or the like

ABSTRACT

The invention relates to a control device for a hydrostatic steering motor of the type having a slide valve arrangement in which inner and outer sleeves are rotatable relative to each other to both sides of a neutral position through a limited small angle. A bypass throttle between the pump and tank connections of the control device has a dual throttle feature which permits the throttle to be closed after only a small amount of turning away from the neutral position and operates with a reduced amount of noise generated during the turning operations for the same total resistance.

The invention relates to a control device for hydrostatic steering meansor the like, comprising a rotatary slide valve arrangement of which theslide elements which are rotatable relatively to each other through alimited angle to both sides of a neutral position comprise controlorifices which form at least a first throttle in the supply to thesteering motor and a second throttle in the return from the steeringmotor, which throttles are closed in the neutral position, as well as abypass throttle that is open in the neutral position and disposedbetween the connections on the pump side and container side.

A control device of this kind with a bypass throttle is known from U.S.Pat. No. 4,096,883. The rotary slide arrangement in that case comprisesan outer and an inner sleeve. The control orifices are formed by thecross-sections of bores, grooves and the like disposed in the peripheralsurfaces of the two sleeves. Behind the first throttle, a load pressureconduit branches off. The particular load pressure serves to control thepump pressure depending on the load and to control a priority valve.

The control device is substantially of the `closed centre` type anddiffers from this only in that in the neutral position a quantity ofpressure fluid limited by the bypass throttle, for example 5% of themaximum amount of throughflow, is passed through the control device.

The parts of the control device are thereby held at a suitabletemperature. It is therefore not possible for jamming to occur when, asa result of starting operations after a prolonged cooling-off period,the slide valve arrangement heats up more rapidly than the housing. Thesteady flow through the control device has the additional advantage thatthe slide in the priority valve keeps the controlled orifice leading tothe control device slightly open. The system is therefore immediatelyready for regulation when the rotary slide valve arrangement of thecontrol device is displaced out of the neutral position. There istherefore no lost motion which the customer experiences as anuncomfortable `hard point` when turning the control device.

In the known case, the bypass throttle is constituted by two controlorifices which are formed by the mouths of an oblique bore in the outersleeve and a radial bore in the inner sleeve. Even in the neutralposition there will be unpleasant noises. Since the drills required toform these bores must have a certain minimum diameter, the controlorifices must have a comparatively large width in the circumferentialdirection. The bypass throttle is therefore still open when the firstthrottle in the supply to the steering motor has already opened. Withthe pump pressure controlled depending on the load, the load pressuretherefore rises and, with it, the pump pressure as long as the bypassthrottle is not yet closed. The higher pressure leads to loud noises.

The invention is based on the problem of providing a control device ofthe aforementioned kind in which less noise is generated.

This problem is solved according to the invention in that the bypassthrottle has two throttle positions behind each other in that twocontrol grooves mutually offset in the direction of rotation areinterconnected in one slide element in the neutral position by abridging space in the other slide element.

By locating the two throttle positions behind each other, there is aconsiderable reduction in noise for the same throttling resistance. Theconstruction also permits the bypass throttle to be completely closedafter turning it by a very small amount out of the neutral position. Forthis, it is only the width of the bridging space and the width of theweb between the mutually offset control grooves that are decisive. It istherefore possible to effect closure before the first and possibly thesecond throttle are opened and the pump pressure rises. This likewisereduces the generation of noise. The production of the control groovesand the bridging space can be undertaken with high precision. Ifdesired, the throttling resistance of the bypass throttle can also beincreased so that, with a given pump pressure, the throughflow throughthe control device can be reduced.

If the rotary slide arrangement comprises an outer and an inner sleeveand the first throttle is formed by circumferentially offset bores inthe outer sleeve and axial grooves separated by webs at the periphery ofthe inner sleeve, it is recommended that the control grooves of thebypass throttle be provided at the periphery of the inner sleeve and thefirst control groove extends in one of the webs. With this arrangement,no additional space is required for the most part of the first controlgroove. In the neutral position, a safe connection to the connection onthe pump side is ensured through the bore associated with the web.

If the interior of the inner sleeve is connected to the connection onthe container side, the second control groove of the bypass throttleshould be formed by a slot through the inner sleeve. The slotestablishes a direct connection to the connection on the container side.

An axially compact construction is obtained if the control grooves ofthe bypass throttle overlap one another. The bridging space can then bekept axially short.

It is particularly favourable if the bridging space is formed by aclosed bore, particularly a blind hole. The latter can also be appliedto the inner circumference of the outer sleeve if it is disposed nearthe end and is drilled slightly obliquely.

If a load pressure conduit branches off behind the first throttle and isin the neutral position connected to the connection on the containerside by way of a relief throttle, it is recommended that the loadpressure conduit should comprise an annular groove which is disposed atthe periphery of the outer sleeve and communicates by way of bores withthe longer axial grooves of the first throttle, that at least one axialgroove should be shorter, that the second control groove of the bypassthrottle should project up to between the longer axial grooves in thevicinity of the shorter axial groove and that the bridging space shouldbe disposed substantially below the annular groove. In this way, it ispossible to apply the bypass throttle so that practically no additionalspace is required.

In a further embodiment of the invention, the relief throttle comprisesa control groove which is disposed at the periphery of the inner sleeveoffset in the direction of rotation adjacent to a longer axial groove ofthe first throttle and axially overlaps the latter, the control grooveand axial groove being interconnected in the neutral position by abridging space at the inner circumference of the outer sleeve.

A preferred example of the invention will now be described in moredetail with reference to the drawing, wherein:

FIG. 1 is a diagramatic representation of a control device that is to beimproved in accordance with the invention,

FIG. 2 is a longitudinal section through a control device according tothe invention,

FIG. 3 is a part-sectional plan view through the outer sleeve of therotary slide arrangement,

FIG. 4 is a section on the line A--A in FIG. 3,

FIG. 5 is a section on the line B--B in FIG. 3,

FIG. 6 is a development of the outer circumference of the outer sleeve,

FIG. 7 is a development of the outer circumference of the inner sleeve,and

FIG. 8 is a graph of the opening surfaces of the throttles against theturning angle.

FIG. 1 diagramatically illustrates a control device 1 for actuating asteering motor 2 which is connected to two steering motor connections Rand L. A connection P on the pump side is connected to a pump 4 by wayof a check valve 2' and the CF connection of a priority valve 3. Aconnection T on the container side is connected to a container 5. Arotary slide valve arrangement contained in the control device 1 isinfluenced on the one hand by a steering wheel 6 and on the other handby a metering motor 7. A total of five throttles is provided in the pathof main flow, namely the throttles A1 to A4 in the supply to thesteering motor 2 and the throttle 5 in the return. The multiplicity ofthrottles is necessary because throttling is to take place in the supplyas well as the return, because the motor connections R and L areconnected to the connection P on the pump side depending on thedirection of rotation of the steering wheel 6, and because the directionof throughflow of the liquid flowing to the steering motor 2 through themetering motor 7 must also take place in dependance on the direction ofrotation. The throttles A1, A4 and A5 are closed in the neutralposition. To this extent, we are concerned with a `closed-centre,non-reaction` steering unit. A load pressure conduit 9 branches off at apoint 8 behind the first throttle A1. A pressure signal LS is derivedfrom the load pressure conduit 9 and, in operation of the steeringmotor, corresponds to the load pressure. The load pressure is limited toa maximum value with the aid of an overflow valve 10 and, on the onehand controls a setting device 11 of the pump 4 which, for example, hasa variable compression to adapt the pump output to requirements, and onthe other hand is supplied to a pressure chamber 12 of the priorityvalve 3. Together with a spring 13, the load pressure here acts on aslide 14 of which the opposite end is impinged by the inlet pressure PPin the pressure chamber 15. The inlet pressure therefore so follows theload pressure LS that the amount of throughflow substantially onlydepends on the opening width of the throttle A1 but not on the loadpressure. Additional consumers can be connected by way of the outlet EFof the priority valve 3.

Between the point 8 and the connection T on the container side, there isa relief throttle 16 which is open in the neutral position but otherwiseclosed. It ensures that the load pressure LS immediately drops to thecontainer pressure when the control device reaches the neutral position.

Between the connection P on the pump side and the connection T on thecontainer side, there is a bypass throttle 17 which opens in the neutralposition but is otherwise closed. When the control device assumes theneutral position, a predetermined small amount of warm pressure fluidwhich keeps the control device at an elevated temperature flows throughthe bypass throttle 17. The actual amount depends upon the throttlingresistance of the bypass throttle and the inlet pressure PP which cannotbe higher than the force of the spring 13 in the priority valve 3.

One embodiment of the invention is shown in more detail in FIGS. 2 to 7.The control device 1 comprises a housing 18 with fitted metering motor 7and an end plate 20. The connection P on the pump side and theconnection T on the container side are provided at the top. The steeringmotor connections R and L are only indicated. The metering motor 7consists of a stationary gear ring 21 having internal teeth and arotating and planetating gear 22 having external teeth, provided betweenthe compression chambers 23.

A rotary slide valve arrangement 25 is disposed in a housing bore 24.This bore contains next to each other an annular groove 26 connected tothe connection T on the container side, an annular groove 27 connectedto the one steering motor connection L, an annular groove 28 connectedto the other steering motor connection R, a series of control orifices29 each connected to a compression chamber 23 by way of an axial passage30, and an annular groove 31 connected to the pump connection P.

The valve arrangement 25 has an outer sleeve 32 and an inner sleeve 33.The outer sleeve 32 is fixed to rotate with the gear 22 of the meteringmotor 7, namely by way of a pin and a cardan shaft 34. The inner sleeve33 is provided with a coupling 35 to connect to the steering wheel 6 andcan therefore be connected thereto to rotate therewith. The two sleevescan be turned relatively to each other through a predetermined angle inboth directions out of a neutral position against the force of radialleaf springs 36.

As shown particularly by FIGS. 3 and 6, the outer sleeve 32 comprises,from right to left, an annular groove 37 with bores 38, an annulargroove 39 with bores 40, a series of bores 41, a double row of bores 42,a double row of bores 43, holes 44 for the passage of the pin forconnecting to the cardan shaft 34, as well as connecting orifices 45.

As will be evident from FIGS. 2 and 7, the inner slide 33 has arrangedtherein from right to left short axial grooves 46 and longer axialgrooves 47 which alternate in a row and are connected to an annulargroove 48 from which further axial grooves 49 extend. They partiallyoverlap with axial grooves 50 which are interconnected by an annulargroove 51 and these overlap partially with axial grooves 52 of whichsome have an aperture 53 for the pin. Both sleeves also have incisions54 and 55 for the leaf springs 36.

As will be evident by viewing FIGS. 6 and 7 together, the bores 40 andand axial grooves 46, 47, form the throttle A1, the axial grooves 49 inconjunction with every second bore 41 form the throttle A2, the axialgrooves 50 in conjunction with the respective other bores 41 form thethrottle A3, the axial grooves 50 depending on the direction of rotationtogether with the bores 42 or 43 form the throttle A4, and the axialgrooves 52 in conjunction with the respective other bores 43 or 42 formthe throttle A5. The bores 40 communicate with the connection P on thepump side by way of the annular groove 31. The bores 41, of which thereare twice the number than there are teeth on the gear 22, together withthe control orifices 29, of which there are as many as there are teethon the gear ring 21, form a distributing valve for the metering motor 7.The bores 42 and 43 communicate with a respective steering motorconnection R and L. The axial grooves 52 by way of a gap 55 provided atthis position between the sleeves and the connecting orifices 45 areconnected to the connection T on the container side.

The bypass throttle 17 is contructed as follows. At the periphery of theinner sleeve 33 there is a first axial control groove 56 and,circumferentially adjacent thereto, there is a second axial controlgroove 57 in the form of a throughgoing slot. They are interconnected inthe neutral position by a bridging space 58 in the form of an obliqueblind bore. The first control groove 56 projects into a web 59 between ashorter axial groove 46 and a longer axial groove 47. Here, itcommunicates with a bore 40 for connection to the inlet pressure PP. Thesecond control groove 57 axially overlaps the first control groove andis provided as an extension of the shorter axial groove 46. Noadditional space is therefore required for the stated components. Only asmall portion of the cross-section of the bridging space 58 covers thecontrol groove 56 and another small portion of its cross-section coversthe control groove 57. Consequently, one obtains two throttlingpositions generating little noise. Turning through a small angle only alittle larger than two degrees will be sufficient to disengage thebridging space 58 fully from one of the two control grooves 56 and 57and thus to close the bypass throttle 17. To produce the relief throttle16, the outer circumference of the inner sleeve 33 is provided with anaxial groove 60 in the form of a throughgoing slot and the innercircumference of the outer sleeve 22 is provided with a bridging space61 in the form of an obliquely drilled blind hole. Since it is importantfor the relief bore to keep the throttling resistance as low aspossible, that is to say to obtain rapid venting, three of the aforesaidconstructions are provided at the periphery. All the bridging spaces aredisposed substantially below the annular groove 37.

FIG. 8 shows the area F of the individual throttles against the turningangle. The neutral positon is at the angle zero. The throttles A2 and A3formed by the control orifices for the metering motor are permanentlyopen. After an angle of about 2 degrees, the throttle A4 opens. Thethrottles A1 and A5 follow. The curve I shows the course of the bypassthrottle 17. It is therefore already closed at an angle of about 2.25degrees when the throttle A1 just starts to open. By way of comparison,the curve II shows the known bypass throttle which only closes at anangle of 4.8 degrees.

Altogether, one therefore obtains a control device in which the bypassthrottle can be produced more accurately than hitherto, is alreadyclosed at a smaller turning angle and greatly surpresses noise. Theblind bore can be produced with a drill of larger diameter than washitherto the case.

Instead of the illustrated `non-reaction` steering unit, one may alsoemploy a `reaction` steering unit in which the two motor connections Rand L are interconnected in the neutral position.

I claim:
 1. A control device for a hydrostatic steering motor,comprising, supply and return pump and tank connections for said device,a slide valve arrangement in which inner and outer slide element sleevesare rotatable relative to each other to both sides of a neutral positionthrough a limited small angle, said sleeves mutually forming controlledsupply and return passages connected to said motor having supply andreturn throttles which are closed when said sleeves are in a neutralposition, bypass throttle means between said pump and tank connectionsbeing open when said sleeves are in a neutral position, said bypassthrottle means having two circumferentially offset throttle positionsformed by two circumferentially offset axially extending bypass throttlegrooves in one of said elements and a bridging recess in the other ofsaid elements.
 2. A control device according to claim 1 wherein saidbypass throttle grooves are formed in the periphery of said innersleeve, said supply throttle being formed by a set of axially extendinggrooves in said inner sleeve and a set of cooperating circumferentiallyspaced bores in said outer sleeve, said set of grooves having separatingweb sections therebetween, one of said throttle grooves being formed asa recess at one end of said inner sleeve and the other of said throttlegrooves being formed within the surface confines of one of said websections.
 3. A control device according to claim 2 wherein the interiorof said inner sleeve has fluid communication with said tank connection,said first one of said throttle grooves being formed as an end slotwhich extends between the inner and outer surfaces of said inner sleeve.4. A control device according to claim 2 including a load pressureconduit branching off behind said supply throttle and being formed as anannular groove in the periphery of said outer sleeve, said supplythrottle grooves comprising alternately arranged longer and shortergrooves, bores in said outer sleeve providing fluid communicationbetween said annular groove and said longer supply throttle grooves,said one of said bypass throttle grooves extending between said longergrooves and said bridging recess being interiorly of and axially alignedwith said annular groove.
 5. A control device according to claim 4including relief throttle passage means between said load pressureconduit and said tank connection, said relief throttle passage meansincluding groove means in the periphery of said inner sleeve alternatelybetween and in axially overlapping relation to said supply throttlelonger grooves, said relief throttle groove means and said supplythrottle longer grooves being interconnected in said neutral position bya bridging recess in the inner surface of said outer sleeve.
 6. Acontrol device according to claim 1 wherein said bypass throttle groovesare in axially overlapping relation to each other.